1. Field of the Invention
This invention relates to a driving circuit for an optical scanner in which light from a light source is reflected and an optical scanner performing a one- or two-dimensional scan with this reflected light is driven.
2. Description of the Related Art
Some of conventional optical scanners are disclosed in Japanese Patent Kokai Nos. Hie 7-175005 and Hie 10-123449. Each of these optical scanners is fabricated by semiconductor manufacturing technology and has the features of compactness and small thickness.
FIG. 1 shows a diagram for illustrating an operating principle of the optical scanner. As shown in this figure, the optical scanner includes a mirror portion 101 in which a coil pattern (a driving coil 102) is provided parallel with a mirror face 101a; spring portions 104a and 104b for oscillating the mirror portion 101; and permanent magnets 105a and 105b arranged close to the mirror portion 101, for producing a magnetic field nearly parallel with the mirror face 101a where the mirror portion 101 is in a stationary state. The spring portions 104a and 104b are connected to a support, not shown, to be fixed to an arbitrary member. By supplying an alternating current (of a frequency t) to the driving coil 102, a force obeying the left-hand rule is generated in a direction normal to the mirror face 101a to oscillate the mirror portion 101 at the frequency f.
When the alternating current is represented by I (=I0 sin (2xcfx80ft)), the strength of the magnetic field by H (a magnetic flux density B), the number of turns of the coil by N, the area of the coil by S, and a vacuum magnetic constant by xcexc0, an oscillating angle xcex8 and a generating force F in this case have the relation expressed by the following equation:
F=xcexc0NHSI0 sin(2xcfx80ft)xc2x7cos xcex8xe2x80x83xe2x80x83(1) 
The oscillating angle xcex8 can be found by solving the following equation of motion:                               θ          ¨                =                                            -              k                        ⁢                          xe2x80x83                        ⁢            θ                    -                      D            ⁢                          xe2x80x83                        ⁢                          θ              .                                +                      F            J                                              (        2        )            
Here, k is a torsion spring constant of the spring portion and has the relation of k=(2xcfx80fc)2, where fc is a mechanical resonant frequency of the optical scanner, D is an attenuation coefficient, and J is the moment of inertia of the optical scanner.
The relation between the oscillating angle xcex8 and the frequency f of the alternating current, in which the oscillating angle xcex8 is thought of as small, can be expressed from Eqs. (1) and (2) by the following equation:                               θ          ⁡                      (            f            )                          =                                                            μ                0                            ⁢                              NHSI                0                                      J                    ⁢                                    1                                                                    {                                          k                      -                                                                        (                                                      2                            ⁢                            π                            ⁢                                                          xe2x80x83                                                        ⁢                            f                                                    )                                                2                                                              }                                    2                                +                                                                            D                      2                                        ⁡                                          (                                              2                        ⁢                        π                        ⁢                                                  xe2x80x83                                                ⁢                        f                                            )                                                        2                                                                                        (        3        )            
FIG. 2A shows a plot of Eq. (3). As shown in FIG. 2A, the maximum oscillating angle (oscillating amplitude) is obtained when the driving frequency f of the alternating current is caused to coincide with the mechanical resonant frequency fc.
From this reason, it is a common practice for the drive of the optical scanner to cause the frequency of a driving signal to coincide with the mechanical resonant frequency of the optical scanner.
In order to stabilize the drive of the optical scanner mentioned above, it is necessary to provide a sensor for detecting the oscillating condition of the optical scanner. In the optical scanner using such a sensor, as disclosed, for example, in Japanese Patent Kokai No. Hie 11-242180, it is known that, in addition to the structure of FIG. 1, a coil pattern (hereinafter referred to as a sensor coil 103), different from the driving coil 102, is provided nearly concentrically on the same plane as the driving coil 102 in the mirror portion 101 (see FIG. 3), and when the mirror portion 101 is oscillated, an electromotive force generated by the interlinkage of the sensor coil 103 with the magnetic field is detected and thereby the oscillating condition is detected.
Here, in the technique of detecting the oscillating condition of the optical scanner of the structure mentioned above, an electromotive force Vr generated in the sensor coil 103 is given by the following equation:
Vr=NsBSs{dot over (xcex8)}xc2x7cos xcex8xe2x80x83xe2x80x83(4) 
where Ns is the number of turns of the sensor coil, B is the magnetic flux density, and Ss is the area of the sensor coil.
Now, consider the case where the optical scanner is driven with the mechanical resonant frequency fc. When the driving signal is expressed as I=I0 sin (2xcfx80fct), the oscillation of the optical scanner is retarded in phase by 90xc2x0 with respect to the driving signal, thus giving
xcex8=xe2x88x92xcex80xc2x7cos(2xcfx80fct)xe2x80x83xe2x80x83(5) 
Therefore, the electromotive force Vr expressed by Eq. (4), in which the oscillating angle xcex8 (xcex80) is thought of as small, can be approximated by the following equation:                                                                         V                r                            =                            ⁢                                                N                  s                                ⁢                B                ⁢                                  xe2x80x83                                ⁢                                  S                  s                                ⁢                                  θ                  0                                ⁢                2                ⁢                π                ⁢                                  xe2x80x83                                ⁢                                                      f                    c                                    ·                  sin                                ⁢                                  xe2x80x83                                ⁢                                                      (                                          2                      ⁢                      π                      ⁢                                              xe2x80x83                                            ⁢                                              f                        c                                            ⁢                      t                                        )                                    ·                  cos                                ⁢                                  xe2x80x83                                ⁢                                  {                                                                                    -                                                  θ                          0                                                                    ·                      cos                                        ⁢                                          xe2x80x83                                        ⁢                                          (                                              2                        ⁢                        π                        ⁢                                                  xe2x80x83                                                ⁢                                                  f                          c                                                ⁢                        t                                            )                                                        }                                                                                                        ≈                            ⁢                                                N                  s                                ⁢                B                ⁢                                  xe2x80x83                                ⁢                                  S                  s                                ⁢                                  θ                  0                                ⁢                2                ⁢                π                ⁢                                  xe2x80x83                                ⁢                                                      f                    c                                    ·                  sin                                ⁢                                  xe2x80x83                                ⁢                                  (                                      2                    ⁢                    π                    ⁢                                          xe2x80x83                                        ⁢                                          f                      c                                        ⁢                    t                                    )                                                                                        (        6        )            
Whereby, it is found that the electromotive force generated in the sensor coil is 90xc2x0 ahead in phase with respect to the oscillation of the optical scanner. (Also, if the connections of both ends of the coil are replaced, the sign of the electromotive force will reverse and the phase will be retarded by 90xc2x0, and the following description is given on the basis of this practice.) Thus, in the resonant frequency drive, the phase relations of the driving signal, the drive of the optical scanner, and the electromotive force of the sensor coil (a sensor signal) are as shown in FIGS. 4A, 4B, and 4C, respectively, and the driving signal (FIG. 4A) coincides in phase with the sensor signal (FIG. 4C).
Here, where the optical scanner is driven at an arbitrary frequency which is much lower than the resonant frequency, the oscillation of the optical scanner, when the driving signal is expressed as I=I0 sin(2xcfx80ft), coincides in phase with the driving signal, thus giving
xcex8=xe2x88x92xcex80xc2x7sin(2xcfx80ft)xe2x80x83xe2x80x83(7) 
Therefore, the electromotive force Vr expressed by Eq. (4), in which the oscillating angle xcex8 (xcex80) is thought of as small, can be approximated by the following equation:                                                                         V                r                            =                            ⁢                                                N                  s                                ⁢                B                ⁢                                  xe2x80x83                                ⁢                                  S                  s                                ⁢                                  θ                  0                                ⁢                2                ⁢                π                ⁢                                  xe2x80x83                                ⁢                                  f                  ·                                      cos                    ⁡                                          (                                              2                        ⁢                        π                        ⁢                                                  xe2x80x83                                                ⁢                        f                        ⁢                                                  xe2x80x83                                                ⁢                        t                                            )                                                        ·                  cos                                ⁢                                  xe2x80x83                                ⁢                                  {                                                                                    θ                        0                                            ·                      sin                                        ⁢                                          xe2x80x83                                        ⁢                                          (                                              2                        ⁢                        π                        ⁢                                                  xe2x80x83                                                ⁢                        f                        ⁢                                                  xe2x80x83                                                ⁢                        t                                            )                                                        }                                                                                                        ≈                            ⁢                                                N                  s                                ⁢                B                ⁢                                  xe2x80x83                                ⁢                                  S                  s                                ⁢                                  θ                  0                                ⁢                2                ⁢                π                ⁢                                  xe2x80x83                                ⁢                                  f                  ·                  cos                                ⁢                                  xe2x80x83                                ⁢                                  (                                      2                    ⁢                    π                    ⁢                                          xe2x80x83                                        ⁢                    f                    ⁢                                          xe2x80x83                                        ⁢                    t                                    )                                                                                        (        8        )            
A common control driving circuit for operating the optical scanner with stability is disclosed in Japanese Patent Kokai No. Hie 09-101474. This control driving circuit has a frequency follow-up control function (a positive feedback control function) for always driving the optical scanner with the resonant frequency and an amplitude control function (a negative feedback control function) for operating the optical scanner with stability at a desired oscillating amplitude.
However, when the control drive of the optical scanner with the sensor is made, the following problem {circle around (1)} arises.
Specifically, the sensor signal (the electromotive force produced in the sensor coil), as shown in Eq. (6) or (8), is proportional to the driving frequency. Consequently, when resonant frequency follow-up control such as that described in Kokai No. Hie 09-101474 is made, the mechanical resonant frequency of the optical scanner fluctuates due to changes of ambience and with age, and thereby the sensor signal is changed, that is, a sensor sensitivity as an oscillating angle sensor is varied, although the oscillating angle is not altered. This gives rise to a vital problem for high-precision amplitude control. Even when the optical scanner is driven at a frequency which is much lower than the resonant frequency, the sensor signal (sensor sensitivity) varies with the driving frequency, and thus the amplitude control becomes difficult.
Briefly described here is a fundamental control driving technique of the conventional optical scanner. An optical scanner 1 is controlled by circuitry shown in FIG. 5. In FIG. 5, from an operating controller such as a PC, not shown, a control signal which is a command value of the desired driving condition of the optical scanner 1, such as the oscillating amplitude (oscillating angle) or oscillating frequency of the optical scanner 1, is supplied to a control circuit 4. The control circuit 4, when receiving the control signal, outputs a driving command signal Vd to a driving circuit 2. The driving circuit 2 outputs a driving signal (the alternating current) to the driving coil 102 in accordance with the driving command signal Vd. The optical scanner 1 is thus oscillated at desired oscillating angle and oscillating frequency. In this case, at both ends of the sensor coil is 5103, when the sensor coil 103 is interlinked with the magnetic field produced by the permanent magnets 105a and 105b, the electromotive force (the sensor signal) is generated. This electromotive force (the sensor signal) is feedbacked to the control circuit 4 as a detecting signal Vs detected by a detecting circuit 3. In the control circuit 4, the detecting signal Vs is monitored so that when the oscillating amplitude (the oscillating angle) or oscillating frequency of the optical scanner 1 is out of a desired value, the driving command signal Vd output to the driving circuit 2 is compensated. In this way, the optical scanner 1 can be controlled and driven with stability.
Subsequently, general constructions of the driving circuit 2 and a detecting circuit 3-a are shown in FIG. 6. As shown in this figure, the driving circuit 2 includes an operational amplifier 201 and a resistance element (R0) 202 so that they convert the driving command signal Vd into the driving signal (the alternating current).
Here, when the driving signal supplied to the driving coil 102 is expressed as I=I0 sin(2xcfx80fct)=I0 sin (xcfx89ct), the relation between the driving command signal Vd and the driving signal (the alternating current) is given by the following equation:
Vd=R0xc2x7I=R0xc2x7I0 sin(xcfx89ct)xe2x80x83xe2x80x83(9) 
The detecting circuit 3-a includes an operational amplifier 301, a resistance element (R1) 302, a resistance element (R1) 303, a resistance element (R2) 304, and a resistance element (R2) 305 so that they convert the electromotive force (the sensor signal) into the detecting signal Vs.
Here, when the electromotive force is denoted by Vr, the resistance value of the sensor coil is denoted by Rsens, and the self-inductance and wiring capacity of the sensor coil 103 are assumed to be negligible, the relation between the electromotive force Vr and the detecting signal Vs is given by the following equation:                               V          s                =                                                            -                2                            ⁢                              R                2                                                                    2                ⁢                                  R                  1                                            +                              R                sens                                              ·                      V            r                                              (        10        )            
However, the conventional optical scanner has the following problem {circle around (2)}.
Specifically, when the driving signal (the alternating current) I is supplied to the driving coil, as shown in FIG. 7, a magnetic field H1 proportional to the driving signal I is produced in a direction perpendicular to the driving coil. In this case, since the conventional optical scanner is such that the driving coil and the sensor coil are nearly concentric and are provided on the same plane, an electromotive force (hereinafter referred to as a mutual induction electromotive force) er attributable to a change of the strength of the magnetic field H1 is generated in the sensor coil. The mutual induction electromotive force er is proportional to a mutual inductance M caused by the driving coil and the sensor coil and the time differential of the driving signal I, and when the driving signal is expressed as I=I0 sin(2xcfx80fct)=I0 sin(xcfx89ct) and a factor of proportionality is denoted by xcex1, it can be expressed by the following equation:                               e          r                =                                            α              ·              M              ·                              I                .                                      ⁢                          xe2x80x83                        ⁢                          (                              or                ⁢                                  xe2x80x83                                ⁢                                                      ⅆ                    I                                                        ⅆ                    t                                                              )                                =                      α            ⁢                          xe2x80x83                        ⁢            M            ⁢                          xe2x80x83                        ⁢                          ω              c                        ⁢                          I              0                        ⁢            cos            ⁢                          xe2x80x83                        ⁢                          (                                                ω                  c                                ⁢                t                            )                                                          (        11        )            
From the above description, it is found that the electromotive force (the sensor signal) actually generated in the sensor coil is not only the electromotive force Vr expressed by Eq. (4), but also the sum with the mutual induction electromotive force er expressed by Eq. (11), namely (Vr+er).
Thus, the true detecting signal Vs is given from Eq. (10) by the following equation:                               V          s                =                                                            -                2                            ⁢                              R                2                                                                    2                ⁢                                  R                  1                                            +                              R                sens                                              ·                      (                                          V                r                            +                              e                r                                      )                                              (        12        )            
and a distorted signal is obtained due to the term of the mutual induction electromotive force er. With this signal, it is difficult to control the oscillating amplitude of the optical scanner with a high degree of accuracy. Also, the phase relations of the driving signal in the resonant frequency drive, the mutual induction electromotive force er, and a true electromotive force (sensor signal) are shown in FIGS. 8A, 8B, and 8C, respectively, and the actual oscillating condition and the sensor signal will be out of phase. This signifies that it becomes difficult to control the oscillating frequency of the optical scanner with a high degree of accuracy.
The control driving circuit of the conventional optical scanner has the following problem {circle around (3)}.
Specifically, the optical scanner mentioned above, theoretically, executes an oscillating motion with single frequency as in Eq. (5) or (7), but actually executes the oscillating motion with a plurality of frequency components, as shown in Eq. (13) or (14) to be described blow, under the influence of an electric noise, mechanical vibrating noise, or magnetic noise.
xcex8(t)=xe2x88x92xcex80{1+xcex1 sin(2xcfx80fxcex1t+xcex8xcex1)}cos(2xcfx80fct)+xcex2 sin(2xcfx80fxcex2t+xcex8xcex2)xe2x80x83xe2x80x83(13)                               θ          ⁡                      (            t            )                          =                                                            θ                0                            ⁢                              {                                  1                  +                                      α                    ⁢                                          xe2x80x83                                        ⁢                    sin                    ⁢                                          xe2x80x83                                        ⁢                                          (                                                                        2                          ⁢                          π                          ⁢                                                      xe2x80x83                                                    ⁢                                                      f                            α                                                    ⁢                          t                                                +                                                  ϕ                          α                                                                    )                                                                      }                            ⁢              sin              ⁢                              xe2x80x83                            ⁢                              (                                  2                  ⁢                  π                  ⁢                                      xe2x80x83                                    ⁢                  f                  ⁢                                      xe2x80x83                                    ⁢                  t                                )                                                    ⏟                              (                I                )                                              +                                    β              ⁢                              xe2x80x83                            ⁢              sin              ⁢                              xe2x80x83                            ⁢                              (                                                      2                    ⁢                    π                    ⁢                                          xe2x80x83                                        ⁢                                          f                      β                                        ⁢                    t                                    +                                      ϕ                    β                                                  )                                                    ⏟                              (                II                )                                                                        (        14        )            
Eq. (13) or (14) is briefly described below. The first term indicated by (I), as shown in FIG. 9A, exhibits a state where an amplitude-modulation noise is produced with respect to a desired oscillating motion of the optical scanner. The second term indicated by (II), as shown in FIG. 9B, exhibits a state where the center of oscillation fluctuates (alternating offset is produced) with respect to the oscillating motion of the optical scanner. An actual oscillating motion of the optical scanner, as shown in FIG. 9C, is in a state where the oscillations of (I) and (II) are superimposed. (Also, in the present invention, the noise of a higher frequency than in the desired oscillating motion of the optical scanner is thought of as negligible. This is because, as seen from the oscillating characteristics of FIGS. 2A and 2B, it is hard to affect the oscillating motion of the optical scanner by the noise of a high frequency.)
Since the control driving circuit of the conventional optical scanner has an amplitude control function for operating the optical scanner with stability at a desired oscillating amplitude, the amplitude-modulation noise of (I) can be eliminated. The optical scanner, however, is constructed so that the fluctuation of the center of the oscillation of (II) cannot be eliminated. As such, there is the problem that the optical scanner cannot be driven with a high degree of accuracy.
Here, referring back to FIG. 6, the relation between the driving command signal Vd and the driving signal I (the alternating current) is given by the following equation:                     I        =                              V            d                                R            0                                              (        15        )            
Although each of a detecting circuit 3-b shown in FIG. 10 and a detecting circuit 3-c in FIG. 11 cannot be expected to provide a detecting function with a high degree of accuracy as in the detecting circuit 3-a of a differential type, it is effective as the detecting circuit and thus its construction is briefly described below.
The detecting circuit 3-b shown in FIG. 10 includes an operational amplifier 310, a resistance element (R3) 311, and a resistance element (R4) 312 so that they convert the electromotive force (the sensor signal) into the detecting signal Vs.
Here, again, when the electromotive force is denoted by Vr, the resistance value of the sensor coil is denoted by Rsens, and the self-inductance and wiring capacity of the sensor coil 103 are assumed to be negligible, the relation between the electromotive force Vr and the detecting signal Vs in the detecting circuit 3-b can be expressed as                               V          s                =                                            R              4                                                      R                3                            +                              R                sens                                              ·                      V            r                                              (        16        )            
The detecting circuit 3-c shown in FIG. 11 includes an operational amplifier 320 and a resistance element (R5) 321 so that they convert the electromotive force (the sensor signal) into the detecting signal Vs.
Here, again, when the electromotive force is denoted by Vr, the resistance value of the sensor coil is denoted by Rsens, and the self-inductance and wiring capacity of the sensor coil 103 are assumed to be negligible, the relation between the electromotive force Vr and the detecting signal Vs in the detecting circuit 3-c can be expressed as                               V          s                =                                            R              5                                                      R                5                            +                              R                sens                                              ·                      V            r                                              (        17        )            
However, the driving circuit of the conventional optical scanner has the following problem {circle around (4)}. As shown in Eqs. (10), (16) and (17), the detecting signal Vs is provided with the resistance value of the sensor coil, and when the resistance value of the sensor coil fluctuates due to a change of ambient and with age, the detecting signal Vs is changed thereby. Furthermore, the sensor coil is placed close to the driving coil, and it is conceivable that the sensor coil is affected by the generation of heat of the driving coil. When the detecting signal Vs is changed by the fluctuation of the resistance value of the sensor coil, it is impossible to detect the oscillating condition of the optical scanner with a high degree of accuracy.
In order to solve the problem {circle around (1)}, it is a first object of the present invention to provide a driving circuit for an optical scanner in which amplitude control can be attained with a high degree of accuracy without undergoing the influence of a change in the driving frequency of the optical scanner.
In order to solve the problem {circle around (2)}, it is a second object of the present invention to provide a driving circuit for an optical scanner in which an operation can be performed with a high degree of accuracy at desired amplitude and frequency by eliminating the mutual induction electromotive force generated in the sensor coil.
In order to solve the problem {circle around (3)}, it is a third object of the present invention to provide a driving circuit for an optical scanner in which the fluctuation of the center of the oscillation of the optical scanner can be eliminated and amplitude control can be attained with a high degree of accuracy.
In order to solve the problem {circle around (4)}, it is a fourth object of the present invention to provide a driving circuit for an optical scanner in which the oscillating condition of the optical scanner can be detected without undergoing the influence of the fluctuation of the resistance value of the sensor coil and amplitude control can be attained with a high degree of accuracy.
In order to achieve the first object, the driving circuit for an optical scanner according to present invention includes a support to be fixed to an arbitrary member; a moving plate, at least one surface of which reflects light; elastic members connecting the support and the moving plate; magnets arranged close to the moving plate at preset distances; a driving coil provided on the moving plate; and a sensor coil provided on the moving plate. In this case, the driving circuit has a current supplying device for supplying a current containing at least an alternating-current component to the driving coil; a detecting device for detecting an induced electromotive force generated in the sensor coil to output a detecting signal corresponding to the induced electromotive force; and a control device for controlling the current supplied to the driving coil by the current supplying device in accordance with the detecting signal output by the detecting device. The control device has an oscillating frequency control device for controlling the frequency of torsional oscillation of the moving plate; a gain circuit for applying gain inversely proportional to the frequency of torsional oscillation of the moving plate to the detecting signal, at least, in the frequency band close to the frequency; and an amplitude control device for controlling the oscillating amplitude of the torsional oscillation of the moving plate in accordance with the output of the gain circuit.
According to the present invention constructed as mentioned above, the gain inversely proportional to the frequency of torsional oscillation of the moving plate is applied to the detecting signal proportional to the frequency, and thereby the oscillating amplitude of the torsional oscillation of the moving plate without undergoing the influence of a change in the driving frequency of the optical scanner. Consequently, the amplitude control can be attained with a high degree of accuracy.
In order to achieve the above object, the driving circuit for an optical scanner according to the present invention is such that the oscillating frequency control device is a resonant frequency follow-up control device for torsion-oscillating the moving plate at the mechanical resonant frequency in accordance with the detecting signal.
According to the present invention constructed as mentioned above, the optical scanner can be torsion-oscillated at the mechanical resonant frequency, and it becomes possible to make the detection of the oscillating amplitude which is not affected by the fluctuation of the mechanical resonant frequency of the optical scanner. Consequently, the amplitude control can be attained with a high degree of accuracy.
Further, in order to achieve the above object, the driving circuit for an optical scanner according to the present invention is such that the gain circuit is constructed with a first-order low-pass filter which has a cut-off frequency much lower than the frequency of torsional oscillation of the moving plate.
According to the present invention constructed mentioned above, the gain inversely proportional to the frequency of torsional oscillation of the moving plate is applied to the detecting signal proportional to the frequency, and gain in a low frequency band can be suppressed. The amplitude control can thus be attained with stability.
Still further, in order to achieve the above object, the driving circuit for an optical scanner according to the present invention is such that the gain circuit is constructed with a first-order band-pass filter which has a cut-off frequency much lower than the frequency of torsional oscillation of the moving plate.
According to the present invention constructed mentioned above, the gain inversely proportional to the frequency of torsional oscillation of the moving plate is applied to the detecting signal proportional to the frequency, and a noise in the low frequency band can be reduced. The amplitude control can thus be attained with a high degree of accuracy.
In order to achieve the second object, the driving circuit for an optical scanner according to the present invention includes a support to be fixed to an arbitrary member; a moving plate, at least one surface of which reflects light; elastic members connecting the support and the moving plate; a pair of magnets arranged close to the moving plate at preset distances; a driving coil provided on the moving plate; and a sensor coil provided on almost the same plane as the driving coil of the moving plate. In this case, the driving circuit has a current supplying device for supplying a current containing at least an alternating-current component to the driving coil; a detecting device for detecting an induced electromotive force generated in the sensor coil; a mutual induction electromotive force generating device for falsely generating a mutual induction electromotive force caused in the sensor coil, independent of the driving coil and the sensor coil, by the current containing at least an alternating-current component which flows through the driving coil; a subtraction device for subtracting the output of the mutual induction electromotive force generating device from the output of the detecting device; and a control device for controlling the torsional oscillation of the moving plate in accordance with the output of the subtraction device.
According to the present invention constructed as mentioned above, the mutual induction electromotive force caused in the sensor coil is falsely generated, independent of the driving coil and the sensor coil, and the torsional oscillation of the moving plate is controlled in accordance with the result that the mutual induction electromotive force falsely generated is subtracted from the induced electromotive force caused in the sensor coil.
In order to achieve the above object, the driving circuit for an optical scanner according to the present invention includes a support to be fixed to an arbitrary member; a moving plate, at least one surface of which reflects light; an elastic member connecting the support and the moving plate; a magnet connected through the elastic member to the moving plate; a driving coil provided to the support; and a sensor coil provided to the support. In this case, the driving circuit has a current supplying device for supplying a current containing at least an alternating-current component to the driving coil; a detecting device for detecting an induced electromotive force generated in the sensor coil; a mutual induction electromotive force generating device for falsely generating a mutual induction electromotive force caused in the sensor coil, independent of the driving coil and the sensor coil, by the current containing at least an alternating-current component which flows through the driving coil; a subtraction device for subtraction-processing the output of the mutual induction electromotive force generating device from the detecting device; and a control device for controlling the torsional oscillation of the moving plate in accordance with the output of the subtraction device.
According to the present invention constructed as described above, the mutual induction electromotive force caused in the sensor coil is falsely generated, independent of the driving coil and the sensor coil, and the torsional oscillation of the moving plate is controlled in accordance with the result that the mutual induction electromotive force falsely generated is subtracted from the induced electromotive force caused in the sensor coil.
Further, in order to achieve the above object, the driving circuit for an optical scanner according to the present invention is such that the mutual induction electromotive force generating device has a first coil and a second coil which are provided on a fixed substrate; a second current supplying device for supplying a current containing at least an alternating-current component to the first coil; and a second detecting device for detecting an induced electromotive force generated in the second coil. The subtraction device subtraction-processes the output of the detecting device and the output of the second detecting device.
According to the present invention constructed as describe above, the mutual induction electromotive force caused in the sensor coil is falsely generated, independent of the driving coil and the sensor coil, by the first and second coils, the second current supplying device, and the second detecting device, and the torsional oscillation of the moving plate is controlled in accordance with the result that the mutual induction electromotive force falsely generated is subtracted from the induced electromotive force caused in the sensor coil.
Still further, in order to achieve the above object, the driving circuit for an optical scanner according to the present invention is such that the mutual induction electromotive force generating device has a first coil and a second coil which are provided on the substrate; a second current supplying device for supplying a current containing at least an alternating-current component to the first coil; and a second detecting device for detecting an induced electromotive force generated in the second coil. The subtraction device subtraction-processes the output of the detecting device and the output of the second detecting device.
According to the present invention constructed as describe above, the mutual induction electromotive force caused in the sensor coil is falsely generated, independent of the driving coil and the sensor coil, by the first and second coils, the second current supplying device, and the second detecting device, and the torsional oscillation of the moving plate is controlled in accordance with the result that the mutual induction electromotive force falsely generated is subtracted from the induced electromotive force caused in the sensor coil.
In the driving circuit for an optical scanner according to the present invention, it is desirable that the mutual inductance caused by the driving coil and the sensor coil is practically equalized to the mutual inductance by the first coil and the second coil.
In doing so, a mutual induction electromotive force which is nearly equal to the mutual induction electromotive force generated in the sensor coil is generated by the first and second coils, the second current supplying device, and the second detecting device, and the torsional oscillation of the moving plate is controlled in accordance with the result that the mutual induction electromotive force generated by the first and second coils, the second current supplying device, and the second detecting device is subtracted from the induced electromotive force generated in the sensor coil.
In the driving circuit for an optical scanner according to the present invention, it is desirable that the first coil is configured into nearly the same structure and shape as the driving coil, the second coil is configured into nearly the same structure and shape as the sensor coil, the second current supplying device is constructed similar to the current supplying device, and the second detecting device is constructed similar to the detecting device.
By doing so, a mutual induction electromotive force which is nearly equal to the mutual induction electromotive force generated in the sensor coil is generated by the first and second coils, the second current supplying device, and the second detecting device, and the torsional oscillation of the moving plate is controlled in accordance with the result that the mutual induction electromotive force generated by the first and second coils, the second current supplying device, and the second detecting device is subtracted from the induced electromotive force generated in the sensor coil.
Further, in order to achieve the above object, the driving circuit for an optical scanner according to the present invention has a first gain circuit increasing or decreasing a current to be supplied through the second current supplying device and a second gain circuit increasing or decreasing an output with the second detecting device.
According to the present invention constructed as mentioned above, a mutual induction electromotive force which is nearly equal to the mutual induction electromotive force generated in the sensor coil is generated by the first and second coils, the second current supplying device, the second detecting device, and the first and second gain circuits, and the torsional oscillation of the moving plate is controlled in accordance with the result that the mutual induction electromotive force generated by the first and second coils, the second current supplying device, the second detecting device, and the first and second gain circuits is subtracted from the induced electromotive force generated in the sensor coil.
Still further, in order to achieve the above object, the driving circuit for an optical scanner according to the present invention is such that the mutual induction electromotive force generating device falsely generates the mutual induction electromotive force caused in the sensor coil, independent of the driving coil and the sensor coil, in accordance with the current supplied to the driving coil.
According to the present invention constructed as mentioned above, the mutual induction electromotive force caused in the sensor coil is falsely generated, independent of the driving coil and the sensor coil, in accordance with the current supplied to the driving coil, and the torsional oscillation of the moving plate is controlled in accordance with the result that the mutual induction electromotive force falsely generated is subtracted from the induced electromotive force caused in the sensor coil.
In the driving circuit for an optical scanner according to the present invention, it is favorable that the mutual induction electromotive force generating device has a phase shifting device for shifting the phase of a signal produced in accordance with the current supplied to the driving coil and a variable gain device for increasing or decreasing the signal produced in accordance with the current supplied to the driving coil.
In doing so, by the mutual induction electromotive force generating device having the phase shifting device for shifting the phase of the signal produced in accordance with the current supplied to the driving coil and the variable gain device for increasing or decreasing the signal produced in accordance with the current supplied to the driving coil, the mutual induction electromotive force caused in the sensor coil is falsely generated, independent of the driving coil and the sensor coil, and the torsional oscillation of the moving plate is controlled in accordance with the result that the mutual induction electromotive force falsely generated is subtracted from the induced electromotive force caused in the sensor coil.
It is favorable that the driving circuit for an optical scanner according to the present invention is provided with at least one of an amplitude control device for continuously controlling the amplitude of the torsional oscillation of the moving plate in accordance with the result of the subtraction device and a frequency control device for continuously controlling the frequency of the torsional oscillation of the moving plate.
By doing so, at least one of the amplitude and frequency of the torsional oscillation of the moving plate is controlled by the control device.
Subsequently, in order to achieve the third object, the driving circuit for an optical scanner according to the present invention includes a support to be fixed to an arbitrary member; a moving plate, at least one surface of which reflects light; elastic members connecting the support and the moving plate; magnets arranged close to the moving plate at preset distances; a driving coil provided on the moving plate; and a sensor coil provided on almost the same plane as the driving coil of the moving plate. In this case, the driving circuit has an oscillation driving device for supplying a current containing at least an alternating-current component to the driving coil to execute a torsional oscillation of the moving plate within a preset angle; an oscillation detecting device for detecting the induced electromotive force generated in the sensor coil, provided with an electromotive force detecting device for outputting a detecting signal corresponding thereto; an oscillating frequency control device for controlling the frequency of the torsional oscillation; a first oscillating amplitude control device for controlling the amplitude of the torsional oscillation in accordance with the detecting signal output by the oscillation detecting device; and a second oscillating amplitude control device for controlling an oscillating condition with each of frequency components except for that of the torsional oscillation in accordance with the detecting signal output by the oscillation detecting device.
According to the present invention constructed as described above, the magnets are arranged in the proximity of the moving plate at preset distances, and the current containing at least an alternating-current component is supplied to the driving coil provided on the moving plate. In this way, a force can be generated in the driving coil provided on the moving plate, and thereby the moving plate can be torsion-oscillated. The oscillation detecting device is capable of detecting the oscillating condition of the moving plate when the electromotive force detecting device detects the induced electromotive force generated in the sensor coil provided on the moving plate. The oscillating frequency control device controls the frequency for torsion-oscillating the moving plate. The oscillation detecting device detects the oscillating condition thereof, and in accordance with this detecting signal, the first oscillating amplitude control device is capable of controlling the amplitude of the torsional oscillation. In accordance with the detecting signal, the second oscillating amplitude control device is capable of controlling the oscillating condition with each of frequency components except for that of the torsional oscillation of the moving plate.
In order to achieve the above object, the driving circuit for an optical scanner according to the present invention includes a support to be fixed to an arbitrary member; a moving plate, at least one surface of which reflects light; an elastic member connecting the support and the moving plate; a magnet connected through the elastic member to the moving plate; a driving coil provided to the support; and a sensor coil provided to the support. In this case, the driving circuit has an oscillation driving device for supplying a current containing at least an alternating-current component to the driving coil to execute a torsional oscillation of the moving plate within a preset angle; an oscillation detecting device for detecting the induced electromotive force generated in the sensor coil, provided with an electromotive force detecting device for outputting a detecting signal corresponding thereto; an oscillating frequency control device for controlling the frequency of the torsional oscillation; a first oscillating amplitude control device for controlling the amplitude of the torsional oscillation in accordance with the detecting signal output by the oscillation detecting device; and a second oscillating amplitude control device for controlling an oscillating condition with each of frequency components except for that of the torsional oscillation in accordance with the detecting signal output by the oscillation detecting device.
According to the present invention constructed as mentioned above, the current containing at least an alternating-current component is supplied to the driving coil provided to the support. In this way, forces can be generated in the magnet connected through the elastic member to the moving plate, and thereby the moving plate can be torsion-oscillated. The oscillation detecting device is capable of detecting the oscillating condition of the moving plate when the electromotive force detecting device detects the induced electromotive force generated in the sensor coil provided to the support.
In the present invention, it is desirable that the second oscillating amplitude control device has a low-pass filter for extracting a frequency component lower than the frequency of the torsional oscillation from the detecting signal and a low-frequency oscillation eliminating device for controlling the oscillating condition of the moving plate so that its output becomes zero.
When the present invention is constructed as described above, the low-pass filter extracts an oscillating motion with a lower frequency than in the torsional oscillation of the moving plate, and the low-frequency oscillation eliminating device makes control so that the output of the low-pass filter becomes zero. Consequently, the oscillating motion with a lower frequency than in the torsional oscillation of the moving plate can be eliminated.
In the present invention, it is desirable that the oscillating frequency control device is provided with a resonant frequency follow-up control device for executing the torsional oscillation of the moving plate at the mechanical resonant frequency in accordance with the detecting signal.
By doing so, the moving plate can be continuously torsion-oscillated at the mechanical resonant frequency.
Subsequently, in order to achieve the fourth object, the driving circuit for an optical scanner according to the present invention includes a support to be fixed to an arbitrary member; a moving plate, at least one surface of which reflects light; elastic members connecting the support and the moving plate; magnets arranged close to the moving plate at preset distances; a driving coil provided on the moving plate; and a sensor coil provided on the moving plate. In this case, the driving circuit has an oscillation driving device for supplying a current containing at least an alternating-current component to the driving coil to execute the torsional oscillation of the moving plate within a preset angle; an oscillation detecting device for detecting the oscillating condition of the moving plate in accordance with the induced electromotive force generated in the sensor coil; an amplitude control device for controlling the amplitude of the oscillation of the moving plate in accordance with the output of the oscillation detecting device; and a frequency control device for controlling the oscillating frequency of the moving plate. The oscillation detecting device has a constant-voltage source connected in series to the sensor coil; a voltage detecting device for detecting voltages created at both terminals of a series circuit comprised of the sensor coil and the constant-voltage source to output signals corresponding thereto; a constant-voltage eliminating device for outputting a signal in which a constant-voltage component is eliminated from the output of the voltage detecting device; and a constant-voltage extracting device for extracting the constant-voltage component from the output of the voltage detecting device to output a signal corresponding thereto.
According to the present invention constructed as described above, in the oscillation driving device, the magnets are arranged in the proximity of the moving plate at preset distances, and the current containing at least an alternating-current component is supplied to the driving coil provided on the moving plate. In this way, a force can be generated in the driving coil provide on the moving plate, and thereby the moving plate is torsion-oscillated. The oscillation detecting device detects the oscillating condition of the moving plate when the electromotive force detecting device detects the induced electromotive force generated in the sensor coil provided on the moving plate. The amplitude control device controls the oscillating amplitude of the moving plate in accordance with the output of the oscillation detecting device. The frequency control device controls the oscillating frequency of the moving plate. In the oscillation detecting device, the voltage detecting device detects the voltages at both terminals of the series circuit comprised of the sensor coil and the constant-voltage source to produce the signal in which the constant-voltage component is eliminated from the result of the detection. Moreover, in the oscillation detecting device, the constant-voltage component is extracted from the output of the voltage detecting device. Since the constant-voltage component obtained here is to indicate the resistance value of the sensor coil, it is possible to know the influence of the fluctuation of the resistance value of the sensor coil on the oscillating condition of the optical scanner.
Further, in order to achieve the above object, the driving circuit for an optical scanner includes a support to be fixed to an arbitrary member; a moving plate, at least one surface of which reflects light; an elastic member connecting the support and the moving plate; a magnet connected through the elastic member to the moving plate; a driving coil provided to the support; and a sensor coil provided to the support. In this case, the driving circuit has an oscillation driving device for supplying a current containing at least an alternating-current component to the driving coil to execute a torsional oscillation of the moving plate within a preset angle; an oscillation detecting device for detecting the oscillating condition of the moving plate in accordance with the induced electromotive force generated in the sensor coil; an amplitude control device for controlling the amplitude of the oscillation of the moving plate in accordance with the output of the oscillation detecting device; and a frequency control device for controlling the oscillating frequency of the moving plate. The oscillation detecting device has a constant-voltage source connected in series to the sensor coil; a voltage detecting device for detecting voltages created at both terminals of a series circuit comprised of the sensor coil and the constant-voltage source to output signals corresponding thereto; a constant-voltage eliminating device for outputting a signal in which a constant-voltage component is eliminated from the output of the voltage detecting device; and a constant-voltage extracting device for extracting the constant-voltage component from the output of the voltage detecting device to output a signal corresponding thereto.
According to the present invention constructed as mentioned above, the oscillation driving device is such that the current containing at least an alternating-current component is supplied to the driving coil provided to the support to thereby generate the forces in the magnet connected through the elastic member to the moving plate. Consequently, the moving plate is torsion-oscillated. In the oscillation detecting device, the electromotive force detecting device detects the induced electromotive force caused in the sensor coil provided to the support, thereby detecting the oscillating condition of the moving plate. The amplitude control device controls the amplitude of the oscillation of the moving plate in accordance with the output of the oscillation detecting device. The frequency control device controls the oscillating frequency of the moving plate. Further, in the oscillation detecting device, the voltage detecting device detects voltages at both terminals of the series circuit composed of the sensor coil and the constant-voltage source to produce the signal in which the constant-voltage component is eliminated from the result of the detection. Still further, in the oscillation detecting device, the constant-voltage component is extracted from the output of the voltage detecting device. Since the constant-voltage component obtained here is to indicate the resistance value of the sensor coil, it is possible to know the influence of the fluctuation of the resistance value of the sensor coil on the oscillating condition of the optical scanner.
Still further, in order to achieve the above object, the driving circuit for an optical scanner according to the present invention, in addition to the above construction of the driving circuit for an optical scanner, is such that the oscillation detecting device is provided with a division device for dividing the output of the constant-voltage eliminating device by the output of the constant-voltage extracting device.
According to the present invention constructed as mentioned above, xe2x80x9cthe signal in which the constant-voltage component is eliminatedxe2x80x9d obtained by the oscillation detecting device can be divided by xe2x80x9cthe constant-voltage componentxe2x80x9d obtained by the oscillation detecting device. Consequently, the oscillating condition of the optical scanner can be found in which the influence of the fluctuation of the resistance value of the sensor coil is excluded.
These and other objects as well as the features and advantages of the present invention will become apparent from the following description of the preferred embodiments when taken in conjunction with the accompanying drawings.